Recently, accompanied with digitization of printing data, a printing plate material for CTP, which is inexpensive, can be easily handled and has a printing ability comparable with that of a PS plate, is required. Particularly, a versatile thermal processless printing plate material, which can be applied to a printing press employing a direct imaging (DI) process without development by a special developing agent and which can be treated in the same manner as in PS plates, has been required.
In a thermal processless printing plate material, an image is formed according to a recording method employing an infrared laser emitting light with infrared to near infrared wavelengths. The thermal processless printing plate material employing this recording method is divided into ablation type, heat fusible type, phase change type, and polymerization/cross-linking type.
Many ablation type printing plate materials have been disclosed (see, for example, Japanese Patent O.P.I. Publication Nos. 8-507727, 6-186750, 6-199064, 7-314934, 10-58636 and 10-244773). These references disclose a printing plate material comprising a substrate and a hydrophilic layer or a lipophilic layer, either of which is an outermost layer. In the printing plate material having a hydrophilic layer as an outermost layer, the hydrophilic layer is imagewise exposed to imagewise ablate the hydrophilic layer, whereby the lipophilic layer is exposed to form image portions.
As the heat fusible type printing plate material, there is one comprising a hydrophilic layer or a grained aluminum plate and provided thereon, an image formation layer containing thermoplastic particles, and a water soluble binder (see, for example, Japanese Patent Publication No. 2938397.). A planographic printing plate material “Thermo Lite” produced by Agfa Co., Ltd. is of this type. Since this type of printing plate material can form an image only by energy necessary to heat fuse, energy for image formation can be reduced and an image can be formed with high speed employing a high power laser.
As the phase change type thermal processless printing plate material, there is a printing plate material comprising a hydrophilic layer containing hydrophobic precursor particles which changes to be hydrophobic at exposed portions, the hydrophilic layer being not removed during printing (see, for example, Japanese Patent O.P.I. Publication No. 11-240270).
As the polymerization/cross-linking type thermal processless printing plate material, there are known printing plate materials (see, for example, U.S. Pat. No. 6,548,222). This type printing plate material employing a roughened surface of an aluminum support increases strength of the image formation layer due to formation of a three dimensional network structure, and exhibits high adhesion of the image formation layer to the support due to anchor effect of the layer with the increased strength, providing greatly improved printing durability.
These printing plate materials for CTP are ones providing a printing plate without development employing a specific processing agent. The influence of the surface configuration of the support on development, printing durability, and stain occurrence is far greater in these printing plate materials requiring no development than in a conventional PS plate, a thermal type CTP or a photopolymer type CTP each requiring development. When the surface of a conventional support is applied to a printing plate material for CTP, strength of an image formation layer and on-press developability are not balanced, providing a printing plate material which is incapable of being subjected to on-press development, or providing a printing plate which is likely to produce stain and is poor in printing durability.
Another prior art of the printing plate material is disclosed in Japanese Patent O.P.I. Publication Nos. 2000-255177 and No. 2001-71654.